Hi,
!!! the information below is not right, take a look at the next reply !!!
I think that, instead of the ipkg-feed you are using, you should use the following feed as a location where ipkg can download packages.
http://ipkg.nslu2-linux.org/feeds/unslung/wl500g/
(edit this path in /opt/etc/ipkg.conf)
The problem is, that the link you provided doesn't host the file you're after.
if you try the link in your browser, a 404 will happen. file not found. that's what ipkg is telling you.
It then suggests you to update to latest information. (because, the package you once were after, is now renamed, and is not available anymore under it's old name.... > ipkg update, so you have new name > download with new file name.. )
!!! The information above is not right, take a look at the next reply !!!
Also, for a great lighttpd/php tutorial look here: http://www.wl500g.info/showthread.php?t=5247
HTH